The present invention relates to a color filter substrate, a method for manufacturing the same, and a liquid crystal display (LCD).
With development of the display technologies, thin film transistor liquid crystal displays (TFT LCDs) have become the mainstream of the display market. Currently, a TFT LCD is developed to have the characteristics of full color, large size, high definition, etc. Color filters are important for a TFT LCD device to realize colorful display. A TFT LCD generally comprises a TFT array substrate, a color filter substrate, and a liquid crystal layer interposed therebetween.
Generally, the color filter substrate is constructed so that a black matrix (BM) is provided on a transparent glass substrate for shielding light, a color filter layer is formed in pixel areas defined by the black matrix, and a transparent conductive layer (counter electrode) of, for example, indium tin oxide is formed on the BM and the color filter layer.
FIG. 1 is a schematic view of the structure of a conventional color filter substrate. As shown in FIG. 1, the conventional color filter substrate comprises a glass substrate 1, a black matrix 2, and a color filter layer 3. The black matrix 2 is provided on the surface of the substrate 1, and the black matrix 2 has a plurality of grid areas, within which the substrate surface is exposed. The grid areas are the pixel areas corresponding to the pixel areas formed on the TFT substrate. The color filter layer 3 is provided in each of the grid areas of the black matrix 2 and also partially overlaps with the black matrix 2, as shown in FIG. 1. A transparent conductive layer 4 (e.g., an ITO layer) covers above the color filter layer 3 and the black matrix 2. The transparent conductive layer 4 as a counter electrode is normally connected with a counter electrode power source, and generates a certain electrical field in corporation with a pixel electrode provided on the TFT substrate that is opposite to the color filter substrate to control the rotation of the liquid crystal molecules and thereby control the transmittance of the liquid layer for displaying an image.
The transparent conductive layer 4 is required to have low sheet resistance and high visible light transmittance. Currently, the transparent conductive layer 4 of the color filter substrate is generally about 1500 Å in thickness and about 20˜30Ω in sheet resistance, which are satisfied for the required display quality of a small size LCD monitor (less than 30 inches). However, for a large size LCD TV set (larger than 30 inches), the influence of large sheet resistance on display quality becomes remarkable, especially on uniformity of display luminance. On the other hand, for a whole LCD device, too large sheet resistance means increased power consumption. An increased thickness of the transparent conductive layer 4 may effectively reduce the sheet resistance, however, increase of the thickness of the transparent conductive layer 4 makes transmittance reduced highly.
In addition, in the conventional color filter substrate, the black matrix 2 and the color filter layer 3 partially overlap with each other to prevent light leakage. Thus, there must be generated a surface step at the positions where the black matrix 2 and the color filter layer 3 overlap with each other. Such step leads to unevenness of the transparent conductive film 4, further causes non-uniformity of the electrical field formed in the central portion and at the edge of the pixel areas and degrades the image quality. FIG. 2 shows the distribution|[zhan1] of the electrical field formed between the two substrates.